The present invention relates to an image forming apparatus which forms an electrostatic latent image on a latent image carrier by using writing electrodes of a writing device, thereby forming the image.
In a conventional image forming apparatus such as an electrostatic copying machine and a printer, the surface of a photoreceptor (photosensitive member) is uniformly charged by a charging device and the charged surface is then exposed to light from an exposure device such as laser beam or LED light, whereby a latent image is written on the surface of the photoreceptor. Then, the latent image on the surface of the photoreceptor is developed by a developing device to form a developing powder image on the surface of the photoreceptor. The developing powder image is transferred to a receiving medium such as a paper, thereby forming the image.
In such conventional image forming apparatus, the exposure device as a writing device for electrostatic latent image comprises a laser beam generating device or a LED light generating device. Therefore, the entire image forming apparatus should be large and complex.
Therefore, an image forming apparatus has been proposed in Japanese Patent Publication No. S63-45104 (hereinafter, ""104B publication) which employs electrodes, as a writing device for forming an electrostatic latent image, to write an electrostatic latent image on a surface of a latent image carrier without using laser beams and LED lights.
The image forming apparatus disclosed in the ""104B publication is provided with a multistylus having a large number of needle electrodes. The needle electrodes are just arranged in contact with an inorganic glass layer on the surface of the latent image carrier. In accordance with an input signal for image information, voltages are selectively applied to corresponding ones of the needle electrodes of the multistylus, whereby the electrostatic latent image can be formed on the latent image carrier. Since the image forming apparatus according to the ""104B publication does not use an exposure device conventionally used as a writing device, the invention of this publication can provide an image forming apparatus which is relatively small in size and relatively simple in structure.
In addition, an image forming apparatus has been proposed in Japanese Unexamined Patent Publication No. H06-166206 (hereinafter, ""206A publication), comprising ion control electrodes which are disposed on a front end portion of an insulating substrate and are arranged in non-contact with a latent image carrier, wherein the ion control electrodes control ions generated by a corona discharger so as to write an electrostatic latent image on the latent image carrier. Since the image forming apparatus according to the ""206A publication also does not use an exposure device as a writing device, the invention of this publication can provide an image forming apparatus which is relatively small in size and relatively simple in structure.
However, in the image forming apparatus according to the ""104B publication, the large number of needle electrodes of the multistylus are just arranged in contact with the inorganic glass layer on the surface of the latent image carrier. It is difficult to keep the stable contact between the needle electrodes and the inorganic glass layer on the surface of the latent image carrier. Accordingly, it is difficult to stably apply charge to the surface of the latent image carrier. This means that it is hard to obtain a high quality image.
Moreover, it is unavoidable to employ an inorganic glass layer on the surface of the latent image carrier for protecting the surface of the latent image carrier from damage due to contacts of a large number of the needle electrodes. This makes the structure of the latent image carrier more complex. In addition, since the inorganic glass layer has quite well physical adsorbed water characteristic, moisture is easily adsorbed by the surface of the inorganic glass layer. Due to the moisture, the electrical conductivity of the glass surface is increased so that electrostatic charge on the latent image carrier should leak. Therefore, the image forming apparatus should be provided with a means for drying the surface of the latent image carrier with adsorbed moisture in order to prevent the apparatus from being affected by absorbed water. This not only makes the apparatus larger but also increases the number of parts, leading to problems of making the structure further complex and increasing the cost.
Since the large number of needle electrodes discharge, the apparatus has another problem that there is a high possibility of generation of ozone (O3). The presence of ozone may not only produce rusts on parts in the apparatus but also melt resin parts because ozone reacts with NOx to generate nitrous acid (HNO3). Again ozone may give an offensive smell. Therefore, the image forming apparatus should be provided with an ventilation system including a duct and an ozone filter which sufficiently exhausts ozone from the inside of the apparatus. This also not only makes the apparatus larger but also increases the number of parts, leading to problems of making the structure further complex and increasing the cost.
On the other hand, in the image forming apparatus according to the ""206A publication, ions produced by the corona discharger are controlled by the ion control electrodes. This means that the apparatus is structured not to directly inject electric charge to the latent image carrier. The invention of the ""206A publication has problems of not only making the image forming apparatus larger and but also making the structure complex. Since the application of charge is conducted by ions, it is difficult to stably write a latent image on the latent image carrier.
Further, since the generation of ions essentially generates ozone, there are problems similar to those described with regard to the image forming apparatus according to ""104B publication.
It is an object of the present invention to provide an image forming apparatus capable of more stably writing an electrostatic latent image and yet achieving reduction in size and reduction in the number of parts thereof so as to have more simple and low-priced structure.
It is another object of the present invention to provide an image forming apparatus capable of further preventing generation of ozone.
In order to achieve these objects, the present invention provides an image forming apparatus which comprises at least: a latent image carrier on which an electrostatic latent image is formed, a writing device for writing said electrostatic latent image on said latent image carrier, and a developing device for developing said electrostatic latent image on the latent image carrier, wherein said electrostatic latent image, written on said latent image carrier by said writing device, is developed by said developing device, thereby forming an image, and is characterized in that said writing device has a plurality of writing electrodes for writing said electrostatic latent image on said latent image carrier and a substrate for supporting said writing electrodes, and that said plurality of writing electrodes are aligned in the main scanning direction of said latent image carrier.
The present invention is characterized in that said writing electrodes are aligned in a single row extending in the main scanning direction of said latent image carrier.
The present invention is further characterized in that said writing electrodes are arranged such that a portion of one writing electrode is overlapped with a portion of a writing electrode, next to the one writing electrode, as seen in the feeding direction of said latent image carrier.
The present invention is still characterized in that said writing electrodes are each formed in a triangle, a parallelogram, or a trapezoid.
Further, the present invention is characterized in that said writing electrodes are each formed in a triangle or a trapezoid and the writing electrodes are arranged in such a manner that the orientations of the triangles or trapezoids of the writing electrodes are alternately inverted.
Furthermore, the present invention is characterized in that said writing electrodes are each formed in a circle, an oval, an ellipse, a rectangle, a square, a pentagon, a polygon having 6 or more corners, or a polygon with rounded corners.
The present invention is characterized in that said writing electrodes are aligned in a plurality of rows each extending in the main scanning direction of said latent image carrier, wherein the rows are arranged in parallel with each other in the feeding direction of said latent image carrier.
The present invention is further characterized in that the number of the parallel rows each extending in the main scanning direction is two and said writing electrodes are arranged in zigzag fashion such that a writing electrode in one row is placed at a position corresponding to a position between two adjacent writing electrodes in the other row while a writing electrode in the other row is placed at a position corresponding to a position between two adjacent writing electrodes in said one row.
Further, the present invention is characterized in that at least said writing electrodes are coated with protecting layers.
Furthermore the present invention is characterized in that at least a portion of each said writing electrode confronting said latent image carrier is made of material easily to wear.
In the image forming apparatus of the present invention having the aforementioned structure, a plurality of writing electrodes are aligned in the main scanning direction of a latent image carrier, thereby making a simple array pattern (electrode pattern) and ensuring an image formation region.
In addition, the writing electrodes are supported by a flexible substrate, thereby stabilizing the positions of the writing electrodes relative to the latent image carrier and thus stably and reliably conducting the application or removal of charge by the writing electrodes relative to the latent image carrier. Therefore, stable writing of an electrostatic latent image is achieved, thus reliably obtaining a high quality image with high precision.
Since the writing electrodes can be securely kept in contact with the latent image carrier with a small pressing force by the flexible substrate or securely kept in proximity to the latent image carrier, the gap (space) between the writing electrodes and the latent image carrier can be extremely reduced. The reduced gap practically reduces the possibility that air existing in the gap is undesirably ionized, thereby further reducing the generation of ozone and enabling the formation of an electrostatic latent image with low potential. In addition, the latent image carrier can be prevented from being damaged by the writing electrodes, thus improving the durability of the latent image carrier.
Further, since the writing device employs only the writing electrodes without using a laser beam generating device or a LED light generating device which is large in size as conventionally used, the apparatus size can be reduced and the number of parts can also be reduced, thereby obtaining an image forming apparatus which is simple and low-price.
The writing electrodes which aligned just in a single row extending in the main scanning direction, thereby making a simple array pattern (electrode pattern) and ensuring an image formation region.
Further, every pair of adjacent writing electrodes which are next to each other are partially overlapped with each other as seen in the feeding direction of the latent image carrier, thereby eliminating such portions in the surface of the latent image carrier that are not subjected to the application or removal of charge and thus achieving uniform application or removal of charge relative to the entire surface of the latent image carrier. Therefore, the occurrence of image defect due to linear stains can be prevented.
The writing electrodes are each formed in a triangle, a parallelogram, or a trapezoid, thereby allowing foreign matters adhering to the surface of the latent image carrier to smoothly and easily pass through spaces between adjacent writing electrodes because the foreign matters can be guided by oblique sides of the triangles, parallelograms, or trapezoids.
Further, the triangular or trapezoidal writing electrodes are arranged in such a manner that the orientations of the triangles or trapezoids of the writing electrodes are alternately inverted. This arrangement enables the triangular or trapezoidal writing electrodes to be efficiently aligned in a compact form in the main scanning direction. This arrangement of alternately inverting the orientations of the triangular or trapezoidal writing electrodes ensures the adjacent writing electrodes to be efficiently partially overlapped with each other in the feeding direction, thereby efficiently and securely exhibiting the effect of overlapping mentioned above.
Furthermore, since the writing electrode can be formed in a circle, an oval, an ellipse, a rectangle, a square, a pentagon, a polygon having 6 or more corners, or a polygon with rounded corners, the writing electrode is flexible to be employed in various types of image forming apparatuses using writing electrodes. In particular, by rounding off corners of a polygon of the writing electrode to eliminate sharp angled portions (edges), the discharge between adjacent writing electrodes can be prevented.
The writing electrodes are aligned in a plurality of parallel rows each extending in the main scanning direction, thereby ensuring the adjacent writing electrodes to be efficiently partially overlapped with each other in the feeding direction, thereby efficiently and securely exhibiting the effect of overlapping mentioned above. In particular, according to the invention defined in claim 8, the writing electrodes are aligned in two parallel rows each extending in the main scanning direction, thus making the arrangement of the writing electrodes more simple, and the writing electrodes in the first and second rows are arranged in a zigzag fashion, thereby easily arranging the writing electrodes while overlapping portions thereof.
Moreover, at least the writing electrodes are coated with the protective layers. The protective layers prevent wear of the writing electrodes and making foreign matters difficult to adhere to the writing electrodes.
In addition, since the portion of the writing electrode confronting the latent image carrier is made of material easily to wear, the portion is shaved by the contact the surface of the writing electrodes relative to the latent image carrier to have a fresh surface so that the surface of the writing electrode can be kept fresh, thus preventing the filming of the writing electrode.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.